Upwardly-acting or roll-up doors are commonly used in trucks, trailers and the like, to selectively close a cargo access opening. These doors generally have a pair of inverted L-shaped tracks, one on either side of the opening. The doors typically have a number (e.g., usually from five to eight) of horizontally-elongated rectangular panels which are series-connected to one another. Thus, the door may be selectively moved between a lowered position in which the panels are vertically-disposed, and a raised position in which the panels are horizontally-disposed in an overhead position.
While this type of door is in common use, a problem persists with respect to cargo shifting against the door and interfering with attempts to raise the same. If not adequately secured, the cargo will normally vibrate and move around during normal over-the-road travel of the vehicle. The problem is accentuated in "wedge"-shaped trailers where the floor is sloped rearwardly toward the cargo opening because the cargo will tend to move toward the door. However, the problem is not limited to vibrational movement, or to "wedge"-shaped trailers. For example, if a backing truck bumps the cargo dock, the inertia of the moving cargo may shift it rearwardly toward the door.
In some instances, shifting cargo becomes interlocked with the door, and hinders or prevents the door from being raised. The principal reason for this is the fact that such door typically has a stepped surface in the vicinity of the hinges. Whether the hinges are mounted on the surface of the door panels and extend into the cargo compartment, or the hinges are recessed in the door, such doors as have been developed heretofore have typically provided an opportunity for shifting cargo to become interlocked therewith.
In addition to this, the several door panels must pass through a space as they are translated from their lowered position to their raised position, and vice versa. For example, when the door is being raised and a panel is arranged at a 45.degree. angle, it forms the hypotenuse of a triangle having equal horizontal and vertical sides. If cargo has shifted into the space through which the panel must pass, operation of the door can be impaired or even prevented. Accordingly, it would be generally desirable to reduce the opportunity for shifting cargo to bear against, and become interlocked with, the lowered door, and to prevent such cargo from entering the space through which the panels must pass as the door is raised.